List of abbreviations

Vocabulary of micros- copic anatomy specialist terms explained in English + German

Every attempt was made to provide correct information and labelling, however any liability for eventual errors or incompleteness is rejected!

dieser Seite Editor: Dr. med. H. Jastrow

Conditions of use

microvilli kidney proximal tubule (monkey)	microvilli kidney proxi- mal tubule (monkey) 2	microvilli + Acinus (exokrine pancreas, monkey)	sensory microvilli of a taste pore  (monkey)

microvilli anchored in the terminal web (rat)	anchored microvilli ileum (rat) 2	anchored microvilli 3 Ileum (monkey)	anchored microvilli 4 enterocyte ileum (monkey)	anchored microvilli 5 ileum (monkey)	microvilli and glycocalyx ileum (monkey)

microvilli goblet cell + Ki- nocilia, trachea (monkey)	microvilli + kinocilia (trachea, monkey) 2	kinocilia and microvilli 3 (monkey)	Kinocilia + Micro- villi cross section (monkey)	Microvilli cross section with glycocalyx (monkey)	Duodenum: Microvilli cross section (monkey)

microvilli + glycocalix 1 (human pharyngeal tonsil)	idem overview	microvilli + glycocalix 2 (human pharyngeal tonsil)	microvilli + glycocalix 3 (human pharyngeal tonsil)	microvilli of the gut (rat)	microvilli of the colon + large glycocalix (rat)

Microvilli (Terminologia anatomica: Mikrovilli) are small finger-like protrusions of the cell membrane towards a lumen that are not actively motile. In many cases microvilli form brush borders consisting of regularly ordered microvilli closely stretching parallel to each other on the surfaces of resorbing epithelial cells. The diameter of a microvillus in a brush border of intestinal cells is about 50 - 100 nm and its length is 1 - 2 µm, however, in other epithelial cells length is about 100 - 200 nm and the diameter is about 50 nm. Bundles of 20 to 40 actin filaments embedded in cytoplasm are present in inside of the microvilli. They are basally connected to the terminal web. Apically the filaments are attached to the thickened cell membrane on top of the microvilli where they are anchored by myosin 1. The actin filaments are bundled with help of fimbrin and villin that also keep them in distance to each other. In the terminal web the actin filaments interact with spectrin and myosin-2 filaments which is supposed to cause smallest movements in order to support resorption of substances from the lumen of e.g., gut. Microvilli strongly increase the cell surface area - about 600 - times and thus raise resorption significantly. Thus the active surface for resorption in an adult gut altogether raises to about 200 m². Lots of different proteins often connected to enzymes are present in the outer membrane of the microvilli which comprises the cell membrane, especially in the gastrointestinal tract. For example lots of different ion channels, amino acid transporters, transporters for glucose and many other substrates. Thus the vast majority of substances which are resorbed in the gastrointestinal tract is taken up into the cytoplasm the area of the microvilli though this cannot be visualised by conventional electron microscopy. Pinocytosis, an uptake (endocytosis) with formation of vesicles, i.e. macropinosomes is only possible in the small areas of the cell membrane located in between the bases of adjacent microvilli. The calcium ion-binding proteins villin and gelsolin are present in the tip regions of microvilli. They may induce a local destruction of the cytoskeleton caused by calcium ion influx e.g., in renal tubules which is followed by an inspecific apocytosis with release of small vesicles into the tubular lumen. In the gut the apex of a microvillus anchors plenty of small interconnected filaments, the antennulae microvillares. The latter form the glycocalyx.

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